Conventionally, there is one that detects a line current by one current sensor on the dc side as a current controlled power converter (refer to, for example, JP 2004-282974 A).
The current controlled power converter theoretically has a phase whose line current cannot be detected and needs to have a current sensor provided for detecting an instantaneous value of a three-phase current on the ac side in order to obtain a dq-axis current by coordinate transformation.
Such a current controlled power converter, in which the current sensor is provided on the ac side, has a problem that, when a current containing a dc component flows, upon connection to an electric power system, through a converter on the system side, a bias magnetism of the converter is caused. According to the “system interconnection technical requirement guideline” of Agency for Natural Resources and Energy, the dc level on the ac side needs to be set not greater than about 1% of the rated ac current.
Therefore, a DCCT capable of detecting the dc component needs to be provided on the ac side for current control of the current controlled power converter in which the current sensor is provided on the ac side, and a low voltage signal outputted from a hall element of DCCT as described above must be amplified by an amplifier. Therefore, it is necessary to employ a DCCT whose amplitude, offset and temperature drift are compensated for with high accuracy, and this leads to a problem of cost increase.